On Tue, Jul 08, 2014 at 02:02:49PM -0400, Jeff Layton wrote:
> Bruce says:
>
> There's also a preexisting expire_client/laundromat vs break race:
>
> - expire_client/laundromat adds a delegation to its local
> reaplist using the same dl_recall_lru field that a delegation
> uses to track its position on the recall lru and drops the
> state lock.
>
> - a concurrent break_lease adds the delegation to the lru.
>
> - expire/client/laundromat then walks it reaplist and sees the
> lru head as just another delegation on the list....
>
> Fix this race by checking the dl_time under the state_lock. If we find
> that it's not 0, then we know that it has already been queued to the LRU
> list and that we shouldn't queue it again.
>
> In the case of destroy_client, we must also ensure that we don't hit
> similar races by ensuring that we don't move any delegations to the
> reaplist with a dl_time of 0. Just bump the dl_time by one before we
> drop the state_lock. We're destroying the delegations anyway, so a 1s
> difference there won't matter.
>
> The fault injection code also requires a bit of surgery here:
>
> First, in the case of nfsd_forget_client_delegations, we must prevent
> the same sort of race vs. the delegation break callback. For that, we
> just increment the dl_time to ensure that a delegation callback can't
> race in while we're working on it.
>
> We can't do that for nfsd_recall_client_delegations, as we need to have
> it actually queue the delegation, and that won't happen if we increment
> the dl_time. The state lock is held over that function, so we don't need
> to worry about these sorts of races there.
>
> There is one other potential bug nfsd_recall_client_delegations though.
> Entries on the victims list are not dequeued before calling
> nfsd_break_one_deleg. That's a potential list corruptor, so ensure that
> we do that there.
>
> Reported-by: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 40 +++++++++++++++++++++++++++++++++-------
> 1 file changed, 33 insertions(+), 7 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 763aeeb67ccf..633b34fd6c92 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1287,6 +1287,8 @@ destroy_client(struct nfs4_client *clp)
> while (!list_empty(&clp->cl_delegations)) {
> dp = list_entry(clp->cl_delegations.next, struct nfs4_delegation, dl_perclnt);
> list_del_init(&dp->dl_perclnt);
> + /* Ensure that deleg break won't try to requeue it */
> + ++dp->dl_time;
> list_move(&dp->dl_recall_lru, &reaplist);
> }
> spin_unlock(&state_lock);
> @@ -2933,10 +2935,14 @@ static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
> * it's safe to take a reference: */
> atomic_inc(&dp->dl_count);
>
> - list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
> -
> - /* Only place dl_time is set; protected by i_lock: */
> - dp->dl_time = get_seconds();
> + /*
> + * If the dl_time != 0, then we know that it has already been
> + * queued for a lease break. Don't queue it again.
> + */
> + if (dp->dl_time == 0) {
Any reason not to just make that
if (dp->dl_time)
return;
?
I don't know if it matters right now, but it might also be useful to
know that no more work will get queued once dl_time is set.
--b.
> + list_add_tail(&dp->dl_recall_lru, &nn->del_recall_lru);
> + dp->dl_time = get_seconds();
> + }
>
> block_delegations(&dp->dl_fh);
>
> @@ -5081,8 +5087,23 @@ static u64 nfsd_find_all_delegations(struct nfs4_client *clp, u64 max,
>
> lockdep_assert_held(&state_lock);
> list_for_each_entry_safe(dp, next, &clp->cl_delegations, dl_perclnt) {
> - if (victims)
> + if (victims) {
> + /*
> + * It's not safe to mess with delegations that have a
> + * non-zero dl_time. They might have already been broken
> + * and could be processed by the laundromat outside of
> + * the state_lock. Just leave them be.
> + */
> + if (dp->dl_time != 0)
> + continue;
> +
> + /*
> + * Increment dl_time to ensure that delegation breaks
> + * don't monkey with it now that we are.
> + */
> + ++dp->dl_time;
> list_move(&dp->dl_recall_lru, victims);
> + }
> if (++count == max)
> break;
> }
> @@ -5107,14 +5128,19 @@ u64 nfsd_forget_client_delegations(struct nfs4_client *clp, u64 max)
>
> u64 nfsd_recall_client_delegations(struct nfs4_client *clp, u64 max)
> {
> - struct nfs4_delegation *dp, *next;
> + struct nfs4_delegation *dp;
> LIST_HEAD(victims);
> u64 count;
>
> spin_lock(&state_lock);
> count = nfsd_find_all_delegations(clp, max, &victims);
> - list_for_each_entry_safe(dp, next, &victims, dl_recall_lru)
> + while (!list_empty(&victims)) {
> + dp = list_first_entry(&victims, struct nfs4_delegation,
> + dl_recall_lru);
> + list_del_init(&dp->dl_recall_lru);
> + dp->dl_time = 0;
> nfsd_break_one_deleg(dp);
> + }
> spin_unlock(&state_lock);
>
> return count;
> --
> 1.9.3
>
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